If you aren't specifying that your perl generated webpage should expire immeadiately, your browser may try to cache it. I don't have the code handy at the moment, but I'm pretty sure its a just a simple one liner you need to add to your code.

*Eg.

use CGI;
 print header(-type=>'image/gif',-expires=>'now',);
[download]

(Alternatively, If using IE, you can disable browser caching by Tools>Internet Options> General Tab > Browsing History Settings button > Select "Never" radio button.)

Pressing Ctrl+F5 should also force your browser to pull a new copy of the page from the server (pressing F5 doesn't necessarily refresh everything, it cheats a bit...)

*Updated: Added code snippit